The only armor you should be able to buy is for TLC; the rest have their own apparel that can be improved and you will have a good idea of when you can do it. Other gear can usually though not always be swapped and you will have plenty of opportunities to change them from many different vendors. Really I don't think you need to worry though. I've played twice and I wouldn't say I was constantly upgrading the gear of my party.

This is very different from most RPGs, even Planescape: Torment. The playing field is more level in violent encounters and those encounters are more risky and less frequent. There trash mobs but they are arguably less frequent than other types. The effort system can be easily abused outside of violent encounters, especially if you are a Nano or Jack. If you have a high edge and effort character in intelligence then you can avoid a lot of troubling situations. It's also handy when the situation becomes violent as many foes can be reasoned with or manipulated while trying to beat you into a bloody pulp.